<%@ page contentType="text/html; charset=utf-8" language="java"
 import="java.sql.*,java.util.*,java.io.*,javax.naming.*,java.awt.image.*,javax.imageio.*,java.awt.*;" errorPage="" %>
<%!
Color getRandColor(int fc,int bc)
{//给定范围获得随机颜色
		Random random = new Random();
		if(fc>255) fc=255;
		if(bc>255) bc=255;
		int rgb=fc+random.nextInt(bc-fc);
		return new Color(rgb,rgb,rgb);
}
%>
<%
		response.setContentType("image/jpeg");
		response.setHeader("Pragma","No-cache");
		response.setHeader("Cache-Control","no-cache");
		response.setDateHeader("Expires", 0); 

//		在内存中创建图象		
		int width=50, height=23;
		BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);

//		获取图形上下文
		Graphics g = image.getGraphics();

//		生成随机类
		Random random = new Random();

//		设定背景色
		g.setColor(getRandColor(250,255));
		g.fillRect(0, 0, width, height);

//		设定字体
		g.setFont(new Font("Times New Roman",Font.PLAIN,18));

//		随机产生155条干扰线，使图象中的认证码不易被其它程序探测到
		g.setColor(getRandColor(225,250));
		for (int i=0;i<155;i++) {
			int x = random.nextInt(width);
			int y = random.nextInt(height);
			int xl = random.nextInt(12);
			int yl = random.nextInt(12);
			g.drawLine(x,y,x+xl,y+yl);
		}

//		取随机产生的认证码(4位数字)
		String sRand="";
		for (int i=0;i<4;i++){
			String rand=String.valueOf(random.nextInt(10));
			sRand+=rand;
//			将认证码显示到图象中
			g.setColor(getRandColor(50,100));//调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成
			g.drawString(rand,10*i+6,16);
		}
		
//		画边框
		g.setColor(new Color(0,153,204));
		g.drawRect(0,0,width-1,height-1);

//		将认证码存入SESSION
		session.setAttribute("syscode",sRand);
//		图象生效
		g.dispose();
		ServletOutputStream responseOutputStream =response.getOutputStream();
//		输出图象到页面
		ImageIO.write(image, "JPEG", responseOutputStream);

//		以下关闭输入流！
		responseOutputStream.flush();
		responseOutputStream.close();
		out.clear();
		out = pageContext.pushBody();
%>
